It will become evident as the description proceeds that the lock of the invention has general utility for use in hotels and motels, as well as, for example, in institutions, industrial plants, governmental facilities, and similar places where changes in the locks are required with some frequency, and where master keying is employed. The lock of the invention is functionally similar to the double-plug double-barrel lock described in U.S. Pat. No. 4,069,694 which issued Jan. 24, 1978 in the names of the present inventors. However, the lock of the invention accomplishes the results of the lock disclosed in the patent with a simpler dual-lock mechanism which is contained entirely within a single plug and barrel.
As mentioned above, two separate and independent locking mechanisms are contained within a single barrel and plug in the lock of the invention. The first locking mechanism is controlled by the #3 key, and the second independent locking mechanism is controlled by the #2 key. In each instance, the #1 key is used to enable the two independent locking mechanisms to be turned to their reset positions by the #2 key or the #3 key, which then permits a new #3 key to be inserted to reset the first locking mechanism to accept only the new #3 key; or a new #2 key to be inserted to reset the second locking mechanism to accept only the new #2 key.
As discussed in the patent, problems have arisen during recent years in preventing theft from hotel and motel rooms due to the unauthorized use of the keys issued to the guests and maids. Such keys are often lost, stolen, or otherwise find their way into the hand of thieves. The problem is aggravated because the prior art hotel keys normally carry identifying tags which gives the thief the exact information as to the name of the hotel, its address, and the room number to which access may be gained by use of the particular key.
A principal object of the present invention is to provide a lock assembly which is constructed to be mounted in existing doors in the place of the previous locks, and which provides a simple and relatively simple mechanism which may be readily reset after each occupancy, so that the previous guest key no longer fits the lock and so that the lock may be quickly set to accept a new guest key. Also, the lock of the invention may be readily reset from time-to-time so that the present maid's key no longer fits the lock, and so that the lock may be set to accept a new maid's key.
The lock to be described is a dual-lock, single-plug type, and it is constructed so that one key may be issued to each guest (#3 key), and a different key may be issued to the maid (#2 key), and so that the maid's key and the guest's key may be used to operate the lock independently of one another, and may be differently coded. Precautions are built into the lock to prevent the guest or maid from resetting the lock, this being achieved by the requirement for the program key (#1 key), which must first be inserted into the lock to turn the plug to a position at which it may be turned to its reset position by either the #2 key or the #3 key to enable the lock to be reset either to accept a new #3 key, or to accept a new #2 key and #1 key. In each instance, the #1 key and the #2 key have the same code, except that the #1 key is shorter than the #2 and #3 keys, so that the #1 key alone can turn the plug in a counterclockwise direction to a particular angular position at which the plug may be turned by either of the other two keys to its reset position.
A feature of the dual lock locking mechanism to be described is the provision of a simple assembly which may be reset at will to receive a different #3 key, or to receive a different #1 and #2 key, this being achieved without the need for any special tools, and merely by turning the lock counterclockwise first by the current #1 key, and then by turning the lock by either the #3 key, or by the #2 key, to the reset position, withdrawing the current key, inserting a new #3 or #2 key, and turning the lock back to its original position by the new key. The lock is thereby set so that it cannot be unlocked by the previous key, but can be unlocked only by the new key. The foregoing operations apply to each section of the dual lock independently of one another.
A feature of the lock of the present invention is that it can be made economically on a mass production basis, as compared with the usual prior art locks. This is because each lock of the present invention can be made exactly the same as all others, and each individual lock need not be designed to accept any one particular key. Moreover, the purchaser of the lock of the invention may change the lock to accept a new key at any time, without the need for any extraneous tools. However, the resetting operation cannot be achieved in the case of a hotel, for example, by the guest himself, or by the maid, since only a person having access to the #1 key is able to reset the lock. Also, as described, the dual lock of the invention has an advantage in that it can be constructed to have approximately the same size as the prior art locks, so that it can be easily mounted into existing door hardware to replace existing locks, without the need for costly adaptation operations.